In the art of refrigerant handling, there is often a need for purging air or other non-condensibles from refrigerant in the refrigerant handling system. U.S. Pat. No. 5,005,369 discloses a system for recovering refrigerant from refrigeration equipment under service with automatic or manual air purge capabilities. This system has enjoyed great commercial acceptance and success for both R-12 and R-134a refrigerant recovery/recycling units in the automotive air conditioner service market. However, the trend in the market, particularly the automotive service market, is toward single service systems that can handle multiple refrigerants. U.S. Pat. Nos. 5,063,749 and 5,181,391 disclose manual purge systems for multiple-refrigerant handling systems, and U.S. Pat. No. 5,285,647 discloses an automatic purge control for a multiple-refrigerant handling system. See also Manz, "How to Handle Multiple Refrigerants in Recovery and Recycling Equipment," ASHRAE Journal, April 1991, pages 22-30, and Manz, The Challenge of Recycling Refrigerants, Business News Publishing, 1995, Chapter 6.
Although the purge control techniques disclosed in the noted patents and publications have enjoyed commercial success and addressed problems theretofore extant in the art, further improvements remain desirable. In particular, there is a need in the art for an automatic purge control technique for use in refrigerant handling systems, particularly refrigerant recovery systems, that are intended and adapted for use in conjunction with multiple differing types of refrigerants having differing pressure/temperature characteristics. It is general object of the present invention to provide a refrigerant handling system and method that address this need in the art.
A refrigerant handling system in accordance with the present invention includes a chamber for holding refrigerant, and a refrigerant pump for directing refrigerant into the chamber so that the refrigerant collects in liquid phase at a lower portion of the chamber while air and other non-condensibles collect in vapor phase at the upper portion of the chamber over the refrigerant. Sensors are responsive to temperatures of the refrigerant entering the chamber and of the refrigerant collected in the lower portion of the chamber. Partial pressure of non-condensibles in the upper portion of the chamber is determined as a function of a difference between such temperatures, and the non-condensibles are purged from the upper portion of the chamber when such partial pressure reaches a selected threshold.
In the preferred embodiments of the invention, the temperature sensors take the form of refrigerant bulbs. A first refrigerant bulb containing refrigerant of preselected type is disposed in heat transferred relationship to refrigerant entering the chamber so that vapor pressure of refrigerant in the first bulb varies as a function of temperature of refrigerant entering the chamber. A second refrigerant bulb containing refrigerant of a second predetermined type, preferably the same refrigerant as in the first bulb, is disposed in heat transferred relationship to refrigerant collected in liquid phase at the lower portion of the chamber so that vapor pressure of refrigerant in the second bulb varies as a function of temperature of refrigerant in the lower portion of the chamber. A purge valve is coupled to the upper portion of the chamber. The valve has a valve element, a spring for urging the valve element to a closed position, and a diaphragm responsive to a pressure differential in combination with the spring for a controlling position of the valve element. The first and second bulbs are connected on opposite sides of the diaphragm in such a way that vapor pressure of refrigerant in the first bulb tends to open the valve element and vapor pressure of refrigerant in the second bulb tends to close the valve element. Thus, when the force of vapor pressure of refrigerant in the first bulb exceeds the sum of the force of vapor pressure in the second bulb plus pressure applied by the spring, the valve element opens to purge non-condensible from within the refrigerant holding chamber.